Method of removing synthetic resin



Patented Aug. 7, 1951 UNITED STATES PATENT OFFICE METHOD OF REMOVINGSYNTHETIC RESIN COATINGS Leopold Pessel, Philadelphia, Pa assignor toRadio Corporation of America. a corporation of Delaware No Drawing.Application April 29, 1947, Serial No. 744,775

essary to strip coatings comprising synthetic resinous materials fromthe ends of wires preparatory to soldering them to terminals or to otherwires. This necessitates a great deal of hand labor by skilled operatorsand, in the case of certain insulation materials, such as polyvinylformal. is an expensive and time consuming procedure. The presentinvention includes discovery of a particular series of compositionswhich may be used to soften even the most resistant synthetic resinmaterials in a matter of seconds. These compositions leave the wire basein a clean and bright state to which a layer 01' solder may immediatelybe applied without subjecting the wire to any further treatment such asthe application of a flux.

One object of the invention is to provide compositions of matter forstripping synthetic resin coatings from any base.

Another object of the invention is to provide compositions forfacilitating the stripping of synthetic resin coatings from a wire base.

Another object is to provide compositions for stripping highly resistantsynthetic resin coatings from copper wire.

Another object is to provide compositions for the rapid softening ofresinous materials comprising one or more of the polyvinyl acetalseries.

Another object of the invention is the provision of an improved methodof preparing a coated copper wire for the reception of solder.

still another object of the invention is the provision of an improvedmethod of preparing a wire to receive solder, using a stripping agent,including pentanedione and a boosting agent.

The various ketones have long been used as solvents for syntheticresinous materials, although even these usually excellent solvents havepreviously been found to have little eflect on certain of the resinousmaterials, especially those of the polyvinyl acetal type. However. infactory processes for applying solder to the ends of wires, it isdesirable to have a material which will soften the insulation and loosenit from the wire so that it may easily be stripped ofi from the ends bythe operator with the aid of fingernails or pliers. In order to bepractical, the stripping material should not be poisonous or generateworkers health or else the installation of expensive airconditioningmeans to make the hazard as small as possible. Heretofore, the fewsolvents which have been used to soften the more resistant types ofsynthetic resin coatings not only generated obnoxious fumes but alsoattacked the wire or left on its surface objectionable deposits whichprevented the application of solder without first removing thesedeposits or subjecting the wire to further steps of preparationresulting in increased processing costs.

poisonous fumes since this entails hazards to the With the presentinvention, however, the discovery has been made of a solvent which canbe used to prepare an insulated wire for soldering which does not supplydangerous fumes nor leave any deposit on the surface of a wire whichwould prevent the successful application of a thin coat of solder. Theparticular material which is used in the practice of this invention ispentanedione. also known as 2,4-pentanedione and also calledacetylacetone, which has the chemical formula CHaCOCHzCOCHs. The efiectof this solvent is particularly pronounced in the case of some of thebaked synthetic resin coatings which yield only with extreme slowness toother solvents. These coating materials are used on modern insulatedconductors due to their toughness and inherent solvent resistance aswell as for their resistance to other deteriorating influences.

The manner in which the improved method may be performed is illustratedin the following example: The end of a copper magnet wire containing athin coating of polyvinyl acetal synthetic resin is dipped in a bath ofpentanedione maintained at F. for about seconds. The wire is removedfrom the liquid, gentl pressure is applied between the nails of thethumb and forefinger and the coating is enabled to be strip d off with asingle motion. The end of' the wire from which the coating has beenremoved is then dipped immediately in a tinning or soldering bath ofconventional composition which provides it with a closely adherentcoating of metal which does not deteriorate on long standing, indicatingthat no corroding deposits have been left on the wire. This tinned orsoldered end may then be immediately soldered to a terminal or toanother wire with no further treating. The solder bath may be 60 percent tin and 40 per cent lead or 40 per cent tin and 60 per cent lead orof any other conventional composition. such as silver soldercompositions.

The time of treatment necessary to soften the coating materialsufiiciently to, be stripped oil with a single motion varies with thetemperature of the bath. With a given polyvinyl acetal coating on No. 30copper wire a treating time oi 3,000

seconds was required at 75 F., 180 seconds at 150 F.. and only 80seconds at 210 F.

This action compares in rapidity to other solvents, such as formic acid,formaldehyde, .or hysystem without changing the optimum treating time bya great deal and at the same time providing a single phase system. Apreferred mutual solvent is diacetone alcohol. A compositioncondroohlorig acid. cheer the prin ipal advantage taming 50 per ,centpentanedione, 25 per cent or using pentane i ne s mp d with previousdiacetone alcohol and 25 per cent water will softening a ts, however, isthat when the p soften an oil-resin enamel coating in about 60 vioussolvents, such as cresylic acid, formic acid, seconds and the polyvinylacetal type in about formaldehyde or concentrated hydrochloric acid,seconds at 150 F. are used they result in corrosion of the wire and i0Although many different types of mutual solthis makes more difficult thepp ic tion of a vents for pentanedione and water were tried, timling' orsoldering coat. They giveofi none was founduvhich had any adverseeffect, fumes which are hazardous to the health of the their inclusionwhen used in amounts up to 25 operators. Other known organic solvents,which per t g l i g d t softening eflect have no deleterious effects onhe W re, do O of the pentanedione and water enough to make compare inrapidi y f action With he co p their use impractical. Besides diacetonealcotions of t e presentinventionhol, other ketones such as acetone,acetonyl ace- A ho h pentanedione, o wa found to tone, etc., are almostequally applicable. Esters have a beneficial action in the preparing ofwires such as methyl lactate, ethyleneglycolm for soldering, 'theaddition of certain booster 20 ethyl-ether, ethyl lactate, etc., may beused, agents as o n o decrease e y the time Alcohols, such as ethylalcohol, isopropyl alco- 01 t p boosting agent, which hol ortetrahydrofurfuryl alcohol, or others, bereatly ac e the action of pentsides diacetone alcohol, have been found almost is water. At roo temp ap to 5 per equally advantageous and other miscellaneous ce t, Water y bemixed with pentanedione mutual solvents for pentanedione and water,without the two materials separating into a such as gamma-Valeralactone, propylene oxide two-ph System Higher a unts of Wate and dioxanehave all been tried and found op may be. added if the temperature isincreased. tiv When used at 150 F., a b comprising 95 Although theinvention is perhaps most valuper cent pentanedione and 5 per cent waterable when used with such coatings as the polylowers the softening timeupon polymerized oilvinyl acetal resins or polymerized oil-resin resinenamels to 120 secon st dec s he enamels, since these are extremelydiflloult to softening time of resins of the po yv nyl acetal remove bymeans previously proposed, .these type to about 90 .seconds. With 90 perce softening agents exert a dissolving or softening pentanedione and 10per C t Water, the action on synthetic resins in general and haveSponding Softening times for the tWO difiel'ent particular applicationin preparing any wire coattypes of coatings were 9 a 60 Seconds, De edwith a synthetic resinous material for the iv y. For the 75 P centpentanedione application of solder. Besides those resins aland 25 percent Water the times are y ready mentioned, there have been used resinsof 30 and 12 seconds under similar tempera e 0 the phenolic type such asphenol formaldehyde, ditions. The accelerating effect is thus seen topolymerized'allyl esters, copolymers of styrene I rise with the amountof water added, in amounts and allyl esters, furane resins,superpolyamides, (if wat D to at least P Of the Denalkyds, melamineformaldehyde, etc'. Although tanedione. Wate u has a o some of theseresins may be softened with other 3' no softening action 1113011 thesematerialssolvents, it is advantageous to be able to soften The additionof water to this system and the them rapidly t a t m which leaves noaccelerating effect of water on the pentanedione unwanted residue afterthe coating is stripped is, thereiore, ent{re1y unexpected from the wireand, in general, the compositions 53in deslrable to have composltlon ofthe present invention are considerably faster which will not separateinto two'phases at room a in action temperatures in to avoidmconvemetlce With the phenolic type resins of equal coatin" storage,compositions were sought whlch tm k Q th fte tim d would have thedesired low treating time at pracmg f mks, i 50 hing e was foun t ticalelevated temperatures and which would rebe Ponslderably 1ee$ than th poyvlnyl acetal m in a Single phase even ft Standing at 55 resins andsoftening of slllcone resins took room temperatures F.) for long periodsof Place In about one-slxth the time required to time. It was found thatmutual solvents for soften Polyvinyl ecetel resins With p ntanedionepentanedione and water may be added to the alone.

Pentanedione, 50 I Pentanedione,75 Diacetone Al- Wire Gage Peptane'water 25 v v t r Type of Coating 8218:1868

Se ests eats? 50 20 2.5 20 2.5 30 5,0 150 1.0 60 3.0 90 2.0 SiliconeResin 30 15 2.0 20 1.5 Allyl Ester Resin 240 30 8.0 30 6.0 StyreneCopolymer Resin 30 .10 3.0 l0 3.0 Furane Resin 300 60 5.0 80 3.7Polymerized Oil Enam 25 10 2.5 15 1.7 Superpolyamide 4,000 180 22.0 18022.0 Alkyd Type Enamel 10 5 2 5 2 Gloss Rod Melamine Formaldehyde Resin.60 15 4.0 20 3.0

.wf'hue The'preceding table shows the softening time for various resinsat 150 F., using compositions comprising either penta'nedione alone,pentanedione and water, orpentanedione, diacetone alcohol and water. iThe Boosting Factor is obtained by dividing the softening time withpentanedione, alone, by the softening time required for thecorresponding resin composition when using the composition with boosteradded. This table also indicates that the compositions of this inventionare useful not only in stripping resin coatings from wires but fromother surfaces such as aluminum sheets, glass rods or wood penels. Thesurfaces listed are merely illustrative and may comprise anything towhich synthetic resins are commonly applied as coating materials.

The data given in the examples were. obtained using coatings ofcomparative thickness using commercially available magnet wires. It hasalso been found that the thickness of the coating also determines thespeed of softening, the thinner the coating, the more rapid thesoftening action providing the same diameter of wire is used. Forunexplained reasons, in extremely thin wires, an increase in softeningtime has been found with decreased wire diameter.

It has beennoted that the boosting effect of the water on the softeningaction of the pentanedione increases practically in direct proportion toits content in the compositions up to 50 per cent water or higher but,when using the higher percentages of water, it is necessary to raise thetemperature of the compositions to inconvenient points in order toprevent the separation of the mixtureiintotwo phases. None of the mutualsolvents for water and pentanedione which have been used in thecompositions, when used alone, has been found to have any significantsoftening effect on the resistant types of resinous materials.

In general, the optimum amount of mutual solvent to be added to thecompositions varies with the mutual solvent selected. In a compositioncomprising pentanedione and water in a 2:1 ratio, for every 1 part ofdiacetone alcohol, for example, there would be needed only 08 part ofisopropyl alcohol. 0.7 part of tetrahydrofurfuryl alcohol but 1.4 partsof gamma-valero lactone. The addition of more than the optimum amountsof the various mutual solvents exerts a diluting efiect and suchproportions may be used to lower the cost of the resulting compositions.

As examples of compositions which contain a higher proportion of mutualsolvent but which still have a rapid softening action, there may be usedpentanedione 30 per cent, water 15 per cent, and diacetone alcohol 55per cent, or pentanedione 10 per cent, water 10 per cent, and diacetonealcohol 80 per cent. These proportions and the proportions in allprevious examples are by volume. The larger percentage of diacetonealcohol serves a definitely useful purpose other than lowering the costin those cases where the material is to be stored at temperatures below70 F. since higher relative amounts of the mutual solvent are thenrequired to prevent separation.

There has thus been described a series of comcoating with a softeningagent comprising 2,4-

pentanedione 50-95 per cent by volume and water 5-50 percent by volumeuntil said coating is softened a predetermined amount and then wipingsaid coating from said surface.

2. A method of stripping a synthetic resinous coating from a metal basematerial comprising treating said coated base material with a softeningagent comprising 2,4-pentanedione 50-95 percent by volume and water 5-50percent by volume and wiping said coating from said surface.

, 3. A method according to claim 2 in whichsaid metal base is copper.

, 4. A method according to claim 2 in which said,

softening agent is maintained at an elevated temperature below theboiling point of said agent.

5. The method of claim 1 in which said coating coating from said wire.

8. A method according to claim 7 in which said resinous coating consistsessentially of a polyvinyl acetal. V

LEOPOLD PESSEL.

REFERENCES CITED The following references are of record in th file ofthis patent:

UNITED STATES PATENTS Number v Name Date 1,653,805 Housekeeper Dec. 27,1927 1,726,623 Hollnagel Sept. 3, 1929 1,884,765 Lougovoy Oct. 25, 19322,242,106 Buckman May 13, 1941 2,417,468 Canziani Mar. 18, 19472,435,239 Schub Feb. 3, 1948 2,438,038 Craver -1 Mar. 16, 1948 OTHERREFERENCES Condensed Chem. Dictionary, Reinhold Pub]. Co., New York, 3rdedition (1942), page 45.

Synthetic Organic Chemicals, booklet of Carbide and Carbon Chem. Corp.,N. Y., 12th ed. (1945), pages 53 and 54. I

Synthetic Organic Chemicals, booklet of Carhide and Carbon ChemicalCorp., N. Y., 12th ed. (1945), pages 56 and 57. i

1. A METHOD OF STRIPPING A SYNTHETIC RESINOUS COATING FROM A SURFACECOMPRISING TREATING SAID COATING WITH A SOFTENING AGENT COMPRISING2,4PENTANEDIONE 50-95 PER CENT BY VOLUME AND WATER 5-50 PERCENT BYVOLUME UNTIL SAID COATING IS SOFTENED A PREDETERMINED AMOUNT AND THENWIPING SAID COATING FROM SAID SURFACE.